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net: mctp: defer creation of dst after source-address check

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Sashiko reports:

> mctp_dst_from_route() increments the device reference count by calling
> mctp_dev_hold(). When a valid route is found and dst is NULL, the
> structure copy is bypassed and rc is set to 0.

Instead of optimistically creating a dst from the final route (then
releasing it if the saddr is invalid), perform the saddr check first.

This means we don't have an unuecessary hold/release on the dev, which
could leak if the dst pointer is NULL. No caller passes a NULL dst at
present though (so the leak is not possible), but this is an intended
use of mctp_dst_from_route().

Signed-off-by: Jeremy Kerr <jk@codeconstruct.com.au>
Reviewed-by: Simon Horman <horms@kernel.org>
Link: https://patch.msgid.link/20260403-dev-mctp-dst-defer-v1-1-9c2c55faf9e9@codeconstruct.com.au
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
This commit is contained in:
Jeremy Kerr
2026-04-03 10:24:51 +08:00
committed by Jakub Kicinski
parent 70e32aadb5
commit f32ba09631
1 changed files with 11 additions and 11 deletions
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22
net/mctp/route.c
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@@ -897,7 +897,8 @@ static mctp_eid_t mctp_dev_saddr(struct mctp_dev *dev)
/* must only be called on a direct route, as the final output hop */
static void mctp_dst_from_route(struct mctp_dst *dst, mctp_eid_t eid,
unsigned int mtu, struct mctp_route *route)
mctp_eid_t saddr, unsigned int mtu,
struct mctp_route *route)
{
mctp_dev_hold(route->dev);
dst->nexthop = eid;
@@ -907,7 +908,7 @@ static void mctp_dst_from_route(struct mctp_dst *dst, mctp_eid_t eid,
dst->mtu = min(dst->mtu, mtu);
dst->halen = 0;
dst->output = route->output;
dst->saddr = mctp_dev_saddr(route->dev);
dst->saddr = saddr;
}
int mctp_dst_from_extaddr(struct mctp_dst *dst, struct net *net, int ifindex,
@@ -975,7 +976,6 @@ int mctp_route_lookup(struct net *net, unsigned int dnet,
{
const unsigned int max_depth = 32;
unsigned int depth, mtu = 0;
struct mctp_dst dst_tmp;
int rc = -EHOSTUNREACH;
rcu_read_lock();
@@ -996,15 +996,15 @@ int mctp_route_lookup(struct net *net, unsigned int dnet,
mtu = mtu ?: rt->mtu;
if (rt->dst_type == MCTP_ROUTE_DIRECT) {
mctp_dst_from_route(&dst_tmp, daddr, mtu, rt);
mctp_eid_t saddr = mctp_dev_saddr(rt->dev);
/* cannot do gateway-ed routes without a src */
if (dst_tmp.saddr == MCTP_ADDR_NULL && depth != 0) {
mctp_dst_release(&dst_tmp);
} else {
if (dst)
*dst = dst_tmp;
rc = 0;
}
if (saddr == MCTP_ADDR_NULL && depth != 0)
break;
if (dst)
mctp_dst_from_route(dst, daddr, saddr, mtu, rt);
rc = 0;
break;
} else if (rt->dst_type == MCTP_ROUTE_GATEWAY) {